Efficient WO3 photoanodes fabricated by pulsed laser deposition for photoelectrochernical water splitting with high faradaic efficiency

In this work, we present a systematic study on the synthesis of monoclinic gamma-WO3 obtained using pulsed laser deposition (PLD). A photocurrent of 2.4 mA/cm(2) (60% of the optical maximum for a 2.7 eV gap material) was obtained for films as thick as 18 mu m. FE-SEM images revealed that WO3 films were actually formed by an array of oriented columns. Efficient hole extraction toward the electrolyte was observed and attributed to a possible accommodation of the electrolyte between the WO3 columns, even for relatively compact films. This feature, combined with the detailed optical absorption and IPCE characterization, allowed us to implement a double-stack configuration of WO3 photoanodes which resulted in a remarkable photocurrent density of 3.1 mA cm(-2) with 1 sun AM1.5 G illumination in 0.1 M H2SO4 electrolyte. Faradaic efficiencies of more than 50% was obtained without co-catalyst, which is one the highest values reported for pure WO3. By adding a 3 nm layer of Al2O3 by ALD, a faradaic efficiency of 80% was reached without diminishing the photocurrent density. (C) 2016 Elsevier B.V. All rights reserved.